Image Processing Apparatus and Method

1. An image processing apparatus for embedding information in an image, comprising: an obtaining section, arranged to obtain distribution information of pixel values of a neighborhood of grid points of an image subjected to a pseudo halftone process, by scanning the image; a detector, arranged to detect an information size of information that can be embedded in the image on the basis of the obtained distribution information; and an embedding section, arranged to embed the information in the image by controlling pixel values on the grid points, except for a grid point in a middle-density region of the image, which is indicated by the obtained distribution information, so that a combination of the controlled pixel values on the grid points indicates the information to be embedded.

2. The apparatus according to claim 1 , further comprising a display section, arranged to display the detected information size on a monitor.

3. An image processing method for embedding information in an image, comprising the steps of: obtaining distribution information of pixel values for a neighborhood of grid points of an image subjected to a pseudo halftone process, by scanning the image; detecting an information size for information that can be embedded in the image on the basis of the obtained distribution information; and embedding the information in the image by controlling pixel values on the grid points, except for a grid point in a middle density region of the image, which is indicated by the obtained distribution information, so that a combination of the controlled pixel values on the grid points indicates the information to be embedded.

4. The method according to claim 3 , further comprising the step of displaying the detected information size on a monitor.

5. A computer readable medium on which is stored computer program code of a method for embedding information in an image, said method comprising the steps of: obtaining distribution information of pixel values of a neighborhood of grid points of an image subjected to a pseudo halftone process, by scanning the image; detecting an information size for information that can be embedded in the image on the basis of the obtained distribution information; and embedding the information in the image by controlling pixel values on the grid points, except for a grid point in a middle density region of the image, which is indicated by the obtained distribution information, so that a combination of the controlled pixel values on the grid points indicates the information to be embedded.